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Welding 304SS Headers

05-13-2009, 10:46 PM

I'm building a set of 304SS headers and I'm using a Diversion 165. I've been practicing quite a bit, but my question is if I only use enough filler rod to keep my puddle going, is the weld going to be strong enough??? I dab a little push the weld a ways and then dab a little more... I can make the weld look very pretty with this method, but I want it to be strong as well...

Another question, if the butt weld joints are perfect with absolutely no gaps, is filler rod even required????

It depends. The throat of your weld should be as thick as the base material. If it's thinner, it will crack from thermal strain.

As for "perfect fitup," you can make autogenous welds from the outside edge (imagine welding the seam of a box-you weld from the outside) pretty readily because you are welding the root. But with headers, the root is inside the tubing. You should leave enough gap to have a keyhole going and fill it with rod. Otherwise, you will not fuse the root and it will seed cracks through.

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Comment

the weld bead is best if it can be slightly raised from the surface. The 304 will expand and contract quite a bit and is prone to cracking especially in high heat applications like turbo's.

I have seen some on Nissans and other last 6 months if luck and these are factory made units like HKS and such.

I have made several out of mild steel and have held up very well. One is 2 years old on a turbo charged car. Schedule 40 1.25" mild steel weld els with 1.25 mild steel pipe for the straights. 3/8th flange on head and 1/2 flange for turbo.

Comment

I'd probably do a few test welds on short sections (I know, SS is expensive!) cut them apart and see what kind of results you're getting. That will provide you with answers better than we can, without knowing your skill level and execution. I built some mild steel headers a few years back, and was amazed at the penetration I had on 14 GA tubing.
A tip for you: A tuned header is going to make the best performance results. Strive for equal length primary tubes. They can be difficult to measure, but I came up with a trick that worked extremely accurately: I put a rubber plug in one end of the tube and filled the tubes with water. By measuring how much water each tube holds, you can calculate its length. My headers turned out not varying by more than 1/2" shortest to longest!
Not a great shot of the header, but here:

Comment

Just wanted to add a cool little idea i came up with ( or started using, I"m probably not the first) but go to the hardware store and get some of those expanding rubber plugs for closing off pipe ends and put one in one end of the tube you're working on but take the bolt out or leave it loose so the air can be pushed out, then take another one and push it in with the bol removed also and screw the end of an argon hose into it these were teh cheapest and best ways to adapt back gassing to pipe that i've found to this day ( i used tape on the ends as recomended in a book i read but got tired of cleaning tape residue off materials that got hot and melted the tape sticky stuff making it hard to remove)

As for solarflux B, I love it, I mena flux isn't quite as good as back gassing, but I've talked to a lot of other old timer fab guys that build headers and most said they went to the solarflux to save argon, save time, and to get rid of the clutter and help make fit up easier without the purging lines being there.

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Comment

It depends. The throat of your weld should be as thick as the base material. If it's thinner, it will crack from thermal strain.

As for "perfect fitup," you can make autogenous welds from the outside edge (imagine welding the seam of a box-you weld from the outside) pretty readily because you are welding the root. But with headers, the root is inside the tubing. You should leave enough gap to have a keyhole going and fill it with rod. Otherwise, you will not fuse the root and it will seed cracks through.

I butt the ends, but bevel to approximately half the thickness of the tubing and back purge. I've used the Solar Flux, but the puddle develops a film that makes it sluggish and you get a hard coating of flux on the inside.

When welding a "bend", the tubing is much thicker on the inside of the radius, so adjust the bevel accordingly.

Comment

Just wanted to add a cool little idea i came up with ( or started using, I"m probably not the first) but go to the hardware store and get some of those expanding rubber plugs for closing off pipe ends and put one in one end of the tube you're working on but take the bolt out or leave it loose so the air can be pushed out, then take another one and push it in with the bol removed also and screw the end of an argon hose into it these were teh cheapest and best ways to adapt back gassing to pipe that i've found to this day ( i used tape on the ends as recomended in a book i read but got tired of cleaning tape residue off materials that got hot and melted the tape sticky stuff making it hard to remove)

I have used rubber plugs, armaflex insulation, foam packing material, cut out with a homemade cookie cutter. I liked the foam or armaflex ones the best as they were cheap to make and scrap material plentiful.
On dairy tubing, I used heavy aluminum foil on the fitting as the tangents were only 1/2" long and they do get hot. Tape will work on a long tangent ferrule, but as you said it is difficult to remove unless done while its still warm.

300 series Stainless will crack much quicker than carbon steel, and if it isnt purge welded and 100% penetration it cracks even easier.

I have made a few exhaust systems (purged) and they lasted the life of the vehicles, I made two different sets of headers for a race car years ago but never heard back if they cracked or not.